In the related art, as shown in FIG. 7, a signal output of a frequency analyzing device or an FFT (Fast Fourier Transform) analyzing device is connected to a command input (for example, a speed command) of a servo, and a detection output of a servo control apparatus, for example, a motor speed, is inputted to the frequency analyzing device. In FIG. 7, 6 denotes a motor, 7 denotes an encoder, 8 denotes a load machine, 12 denotes a servo control apparatus, and 11 denotes an FFT analyzing and measuring device.
The frequency analyzing device outputs a signal, in which a frequency is swept, to the servo control apparatus, performs an FFT analysis on a speed waveform of a motor driven by the servo control apparatus, and obtains a frequency of vibration. Alternatively, frequency characteristic of a servo system is obtained from an FFT analysis result of the swept waveform and the motor speed waveform, and the vibration frequency is specified. A parameter of a vibration suppression filter (for example, notch filter, low pass filter, etc.) for cutting off a resonance frequency is set from the vibration frequency obtained as described above.
For example, a resonance frequency f0 is obtained from a graph of FIG. 5(i), and a cutoff frequency of the filter is combined with f0 as shown in a graph of FIG. 5(ii). In addition, as disclosed in Patent Document 1, a signal in which the frequency is varied and which has a fixed amplitude is inputted to the servo control apparatus, the frequency analysis is performed on the motor speed signal, a position signal of a movable table in a machine, or the like, the resonance frequency is obtained, and a parameter of the filter is determined so as to cut off the resonance frequency.
Patent Document 1: JP-A-05-346813